Tarek,
Yes, there can indeed be overlaps (see page 14 and 32 of the PMBOK Guide).
If you look at this from a VERY high and conceptual level:
The OPA focus on process related information and they define how we do things in our company. They define the processes our project has to follow.
The EEF are factors that will "make or break" our project. They define our success (or failure) factors.
So it's quite possible that there are items that can be found on both sides.